Excitement From The Core - Pontiac’s “All-Block” Engines

​When it comes to the great engines that powered the big three’s vintage muscle cars, lines are usually drawn between two camps, big block or small block. With that said, one manufacturer, originally known as GM’s “performance” division, did things a little differently.
Pontiac Motor Division got it’s first V8 rumbling in 1955 and continued building power plants until 1981. During its heyday decades of the ‘60s and ‘70s, all cubic-inch displacement Pontiac V8 motors utilized the same mid-size cast-iron block. A division that would become known for it’s forward thinking vehicle designs also thought out of the box when it came to engine building.

​Pontiac accomplished this feat of engine efficiency by increasing – or decreasing in some cases – the bore of the cylinders and the piston travel, or “stroke”, creating what they called small or large “journal” engines. The pistons of course, also grew either larger or decreased in size to fit the bore, allowing for multiple cubic-inch displacements from one standard Pontiac block, so technically and actually, there are no big block or small block Poncho motors…ingenious.

​Small Journal motors like the 326cid, 350cid, the famous 389cid or later 400cid, equipped GTOs and Firebirds, while legendary large journal engines such as the 421cid and 428cid were designated to full-size Pontiacs and were more-often worked-up with stronger internals, cranks, rods, mains, etc, into Super Duty motors mainly for racing.
The most famous large journal engine was the 455cid, which debuted in 1970 and was the last of the factory Super Duty’s, built exclusively for the 1973-’74 SD-455 Trans Am, to many, the last of the original muscle cars. So when someone asks about Pontiac engines, at least now you’ll know, that Pontiac didn’t do big-block/small-block.

Article courtesy of Street Muscle Magazine, written by Andrew Nussbaum.